Catheter with integrated controller for imaging and pressure sensing

ABSTRACT

An intravascular ultrasound (IVUS) device that includes a flexible elongate member having a proximal portion and a distal portion; a controller coupled to the distal portion of the flexible elongate member; an ultrasound transducer disposed at the distal portion of the flexible elongate member and in communication with the controller; a pressure transducer disposed at the distal portion of the flexible elongate member and in communication with the controller; and plurality of conductors extending from the controller to the proximal portion of the catheter, at least one conductor of the plurality of conductors being configured to carry both the signals representing information captured by the ultrasound transducer and information captured by the pressure transducer.

The present application is a continuation of U.S. patent applicationSer. No. 14/692,511, filed Apr. 21, 2015, now U.S. Pat. No. 11,311,271,which claims priority to and the benefit of the U.S. Provisional PatentApplication Nos. 61/983,101, filed Apr. 23, 2014, each of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to systems, devices, andmethods employing a controller for both imaging and pressure sensors fordiagnostically assessing a target region of a patient. Moreparticularly, the present disclosure relates to systems, devices, andmethods that utilize a common controller to perform intravascularultrasound (IVUS) imaging and pressure sensing for diagnosticallyassessing a target region of a patient, such as a patient's vasculature,for example.

BACKGROUND

Intravascular ultrasound (IVUS) imaging is widely used in interventionalcardiology as a diagnostic tool for assessing a diseased vessel, such asan artery, within the human body to determine the need for treatment, toguide the intervention, and/or to assess its effectiveness. IVUS imaginguses ultrasound echoes to form a cross-sectional image of the vessel ofinterest. Typically, the ultrasound transducer on an IVUS catheter bothemits ultrasound pulses and receives the reflected ultrasound echoes.The ultrasound waves pass easily through most tissues and blood, butthey are partially reflected by discontinuities arising from tissuestructures (such as the various layers of the vessel wall), red bloodcells, and other features of interest. The IVUS imaging system, which isconnected to the IVUS catheter by way of a patient interface module,processes the received ultrasound echoes to produce a cross-sectionalimage of the vessel where the catheter is located.

There are two types of IVUS catheters in common use today: solid-stateand rotational, with each having advantages and disadvantages.Solid-state IVUS catheters use an array of ultrasound transducers(typically 64) distributed around the circumference of the catheter andconnected to an electronic multiplexer circuit. The multiplexer circuitselects array elements for transmitting an ultrasound pulse andreceiving the echo signal. By stepping through a sequence oftransmit-receive pairs, the solid-state IVUS system can synthesize theeffect of a mechanically scanned transducer element, but without movingparts. Since there is no rotating mechanical element, the transducerarray can be placed in direct contact with the blood and vessel tissuewith minimal risk of vessel trauma and the solid-state scanner can bewired directly to the imaging system with a simple electrical cable anda standard detachable electrical connector.

In the typical rotational IVUS catheter, a single ultrasound transducerelement fabricated from a piezoelectric ceramic material is located atthe tip of a flexible driveshaft that spins inside a plastic sheathinserted into the vessel of interest. The transducer element is orientedsuch that the ultrasound beam propagates generally perpendicular to theaxis of the catheter. The fluid-filled sheath protects the vessel tissuefrom the spinning transducer and driveshaft while permitting ultrasoundsignals to freely propagate from the transducer into the tissue andback. As the driveshaft rotates (typically at 30 revolutions persecond), the transducer is periodically excited with a high voltagepulse to emit a short burst of ultrasound. The same transducer thenlistens for the returning echoes reflected from various tissuestructures, and the IVUS imaging system assembles a two dimensionaldisplay of the vessel cross-section from a sequence of several hundredof these ultrasound pulse/echo acquisition sequences occurring during asingle revolution of the transducer.

While the solid-state IVUS catheter is simple to use, thanks to its lackof moving parts, it cannot match the image quality available from arotational IVUS catheter. It is difficult to operate a solid-state IVUScatheter at the same high frequency as a rotational IVUS device, and thelower operating frequency of solid-state IVUS catheters translates intopoorer resolution compared to that of a higher frequency rotational IVUScatheter. There are also artifacts such as sidelobes, grating lobes, andpoor elevation focus (perpendicular to the imaging plane) that arisefrom the array-based imaging that are greatly reduced or completelyabsent with a rotational IVUS device. Despite the image qualityadvantages of the rotational IVUS catheter, each of these devices hasfound a niche in the interventional cardiology market, with solid-stateIVUS preferred in circumstances where ease-of-use is paramount and thereduced image quality is acceptable for the particular diagnostic needs,while rotational IVUS is preferred where image quality is paramount andthe more time-consuming catheter preparation is justified.

In the rotational IVUS catheter, the ultrasound transducer is typicallya piezoelectric ceramic element with low electrical impedance capable ofdirectly driving an electrical cable connecting the transducer to theimaging system hardware. In this case, a single pair of electrical leads(or coaxial cable) is used to carry the transmit pulse from the systemto the transducer and to carry the received echo signals from thetransducer back to the imaging system by way of a patient interfacemodule, where they are assembled into an image.

Some catheters utilize pressure sensors disposed to assess the severityof a stenosis in a blood vessel, including ischemia-causing lesions. Onemethod for assessing the severity of a stenosis includes taking twoblood pressure measurements with the pressure sensor: one measurementdistal or downstream to the stenosis and one measurement proximal orupstream to the stenosis. The differences in pressure may be used tocalculate a value indicating the severity of the stenosis. Commontreatment options include angioplasty, atherectomy, and stenting.

While existing IVUS catheters and existing pressure sensing cathetersdeliver useful diagnostic information, there is a need for combinedpressure sensing and IVUS catheters that enable a health care providerto efficiently perform diagnostic assessment of multiple ways, such asimaging and pressure sensing while requiring only a single catheter tobe introduced to a patient. There is also a need for combined pressuresensing and IVUS catheters that are integrated together in a manner thateffectively and efficiently conserves space or volume required so thatthe catheter is still sized small enough to access small target areas.

Accordingly, there remains a need for improved devices, systems, andmethods for providing a compact and efficient catheter that has bothultrasound transducers for imaging or determining physical dimensionsand a pressure sensor for measuring the pressure of fluid within a bloodvessel.

The present disclosure addresses one or more of the shortcomings in theprior art.

SUMMARY

Embodiments of the present disclosure provide a compact and efficientcircuit architecture and electrical interface to a polymer piezoelectricmicro-machined ultrasonic transducer used in an intravascular ultrasoundsystem.

In an exemplary aspect, the present disclosure is directed to anintravascular ultrasound (IVUS) device that includes a flexible elongatemember having a proximal portion and a distal portion; a controllercoupled to the distal portion of the flexible elongate member; anultrasound transducer disposed at the distal portion of the flexibleelongate member and in communication with the controller; a pressuretransducer disposed at the distal portion of the flexible elongatemember and in communication with the controller; and a plurality ofconductors extending from the controller to the proximal portion of thecatheter, at least one conductor of the plurality of conductors beingconfigured to carry both the signals representing information capturedby the ultrasound transducer and information captured by the pressuretransducer.

In an aspect, the ultrasound transducer comprises an ultrasoundtransducer imaging element configured to be rotated about an axis of theelongate member. In an aspect, the ultrasound transducer comprises atransducer array formed of a plurality of ultrasound transducers. In anaspect, the plurality of conductors comprises a four-lead electricalcable and the controller is configured to communicate signals based oninformation from both the ultrasound transducer and the pressuretransducer on the same wire. In an aspect, the pressure transducerconnects to the controller via three leads. In an aspect, a distalportion of the four-lead electrical cable is electrically coupled to thecontroller. In an aspect, a proximal portion of the four-lead electricalcable is coupled to a connector configured to connect the four-leadelectrical cable to a patient interface module (PIM). In an aspect, thecontroller is disposed adjacent the ultrasound transducer. In an aspect,the pressure transducer is disposed distal of the ultrasound transducer.In an aspect, the flexible elongate member comprises a guidewire lumenfor receiving a guidewire.

In an exemplary aspect, the present disclosure is directed to anintravascular ultrasound (IVUS) imaging and pressure sensing system,comprising a catheter and a user interface. The catheter includes acontroller disposed at a distal portion of the catheter; an ultrasoundtransducer disposed at the distal portion of the catheter and incommunication with the controller; a pressure transducer disposed at thedistal portion of the catheter and in communication with the controller;and a plurality of conductors extending from the controller toward theproximal portion of the catheter, at least one conductor of theplurality of conductors being configured to carry signals representingboth information captured by the ultrasound transducer and informationcaptured by the pressure transducer. The user interface is incommunication with the catheter and configured to present informationbased on the signals carried by the plurality of conductors.

In an aspect, the ultrasound transducer comprises an ultrasoundtransducer imaging element configured to be rotated about an axis of theelongate member. In an aspect, the ultrasound transducer comprises atransducer array formed of a plurality of ultrasound transducers. In anaspect, the cable is a four-lead electrical cable and the controller isconfigured to communicate signals based on information from both theultrasound transducer and the pressure transducer on the same wire. Inan aspect, the pressure transducer connects to the controller via threeleads. In an aspect, a distal portion of the four-lead electrical cableis electrically coupled to the controller. In an aspect, a proximalportion of the four-lead electrical cable is coupled to a connectorconfigured to connect the four-lead electrical cable to a patientinterface module (PIM).

In an exemplary aspect, the present disclosure is directed to a methodof assessing a patient comprising: receiving information captured by anultrasound transducer disposed at a distal portion of a catheter;receiving information captured by a pressure transducer disposed at adistal portion of the catheter; generating communication signalsrepresenting the information from the ultrasound transducer and from thepressure transducer at a controller carried on the catheter; andtransmitting the communication signals representing both the informationcaptured by the ultrasound transducer and information captured by thepressure transducer from a controller carried on the catheter to a userinterface.

In an aspect, receiving information captured by an ultrasound transducerand receiving information captured by a pressure transducer areperformed simultaneously. In an aspect, transmitting the communicationsignals representing both the information captured by the ultrasoundtransducer and information captured by the pressure transducer comprisestransmitting signals in real time as they are received from theultrasound transducer and the pressure transducer. In an aspect, thegenerating includes converting analog signals received from one of thepressure transducer and ultrasound transducer into digital signals priorto the transmitting.

Some embodiments of the present disclosure establish a circuitarchitecture that provides the needed signal amplification and anefficient pulser circuit, with an electrical interface that requires asmall number of electrical leads. In that regard, a smaller number ofleads allows larger diameter conductors to be used within the limitedspace of the flexible elongate member, resulting in reduced cableattenuation and low electrical loss in the interconnect cable extendingalong the length of the flexible elongate member. Further, embodimentsof the present disclosure provide excellent cable impedance matching. Inthat regard, a four-lead interface facilitates a cable design consistingof a pair of balanced transmission lines, with each transmission lineproperly terminated to minimize reflections and distortion of thefrequency response that can cause artifacts or degradation in the image.Alternatively, a four-lead interface facilitates an alternative cabledesign (shielded twisted triplet) consisting of a one balancedtransmission line, properly terminated to minimize reflections anddistortion of the frequency response that can cause artifacts ordegradation in the image, while the high voltage DC and ground signalsare carried by an unbalanced conductor pair, where impedance matchingand balance are not important.

Further, embodiments of the present disclosure also provide low signalcoupling. For example, the four-lead cable can be operated in a “starquad” configuration with diagonal conductor pairs forming independenttransmission lines. In this configuration, coupling between diagonalsignal pairs, each operated in differential mode, is minimized by thesymmetry of the coupling to provide low cross-talk between the multiplesignals carried by the cable. Also, a shielded twisted triplet cable canbe operated in a configuration with two of the three twisted conductorsforming a balanced transmission line, while the third twisted conductorand the shield carry the high voltage DC and ground signals. In thisconfiguration, coupling between the balanced signal pair operated indifferential mode and the other conductors is minimized by symmetry.

Further still, embodiments of the present disclosure provide lowelectromagnetic interference (EMI). In that regard, the four-leadinterface facilitates a cable design consisting of a pair of balancedtransmission lines. The balanced design inhibits radiation of EMI, aswell as reduces the susceptibility of the system to externalinterference from other devices. The four-lead interface cable isjacketed with an electrical shield conductor in some instances tofurther suppress EMI and susceptibility to external interference. Also,a four-lead interface facilitates a cable design consisting of ashielded twisted triplet, comprised of one balanced signal pair and oneunbalanced pair. This balanced design inhibits radiation of EMI, as wellas reduces the susceptibility to external interference from otherdevices, while the unbalanced pair carries only low frequency signals,not prone to generating EMI. The shielded twisted triplet cable designincludes an electrical shield conductor to further suppress EMI andsusceptibility to external interference.

Embodiments of the present disclosure also provide design flexibility,small integrated circuit die dimensions suitable for use inintravascular catheters and/or guidewires, low power dissipation, hightransmit voltages, and an efficient protection circuit. For example, theuse of a serial communication scheme makes it feasible to addflexibility and advanced features to the circuit design withoutcomplicating the four-lead physical interface between the PIM and thetransducer. The circuit described herein is implemented in a compactapplication-specific integrated circuit (ASIC or controller as usedherein) and the four lead electrical interface consumes only a smallportion of the device area such that the system can be implemented incatheters and guidewires having an outer diameter as small as 0.020″(0.5 mm) in some embodiments. Embodiments of the circuits describedherein are designed to minimize power dissipation to avoid excessivetemperature rise at the distal end of the catheter. Also, embodiments ofthe circuits described herein include a high voltage pulser at thedistal end of the catheter that avoids the significant cable lossesassociated with a PIM-based pulser circuit. This approach also reducesthe EMI that might otherwise be produced by sending a high voltagetransmit pulse through the electrical cable extending along the lengthof the device, connecting the PIM to the transducer. Further,embodiments of the circuits described herein implement an efficientprotection circuit using an actively controlled analog switch to isolatethe sensitive amplifier inputs from the high voltage transmit pulseapplied to the transducer. This analog switch based protection circuitdesign is facilitated by the proximity between the transmitter,amplifier, protection, and timing circuits, all of which are integratedinto a single controller.

Additional aspects, features, and advantages of the present disclosurewill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure will be describedwith reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic schematic view of an imaging system accordingto an embodiment of the present disclosure.

FIG. 2 is a diagrammatic, partial cutaway perspective view of an imagingdevice according to an embodiment of the present disclosure.

FIG. 3 is a diagrammatic, cross-sectional side view of a distal portionof the imaging device of FIG. 2.

FIG. 4 is a diagrammatic side view of components of the distal portionof the imaging device shown in FIG. 3, including a MEMS component and acontroller component, according to an embodiment of the presentdisclosure.

FIG. 5 is a diagrammatic bottom view of the controller component of thecomponents illustrated FIG. 4.

FIG. 6 is a diagrammatic top view of the MEMS component of thecomponents illustrated in FIG. 4.

FIG. 7 is a diagrammatic, cross-sectional side view of a distal portionof an imaging device according to another embodiment of the presentdisclosure.

FIG. 8 is a diagrammatic, schematic view of a distal portion of animaging device according to another embodiment of the presentdisclosure, with the distal portion being arranged in a flatconfiguration.

FIG. 9 is a diagrammatic, schematic view of a distal portion of animaging device according to another embodiment of the presentdisclosure, with the distal portion being arranged in a flatconfiguration.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It is nevertheless understood that no limitation tothe scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, systems, and methods, and anyfurther application of the principles of the present disclosure arefully contemplated and included within the present disclosure as wouldnormally occur to one skilled in the art to which the disclosurerelates. In particular, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure. For the sake ofbrevity, however, the numerous iterations of these combinations will notbe described separately.

The systems, devices, and methods disclosed herein relate to a systemcapable of carrying out both imaging using an ultrasound transducer andpressure sensing using a pressure transducer. As described herein, theultrasound transducer and the pressure transducer share a commonconventional cable and other electrical components. With fewercomponents extending the length of the catheter, the overall diameter ofthe catheter may be smaller than could otherwise be achieved. Inaddition, some manufacturing steps may be eliminated when compared tomanufacturing with distinct IVUS imaging and pressure transducers.

Referring to FIG. 1, shown therein is an IVUS imaging and pressuresensing system 100 according to an embodiment of the present disclosure.In some embodiments of the present disclosure, the IVUS imaging andpressure sensing system 100 is a piezoelectric micromachined ultrasoundtransducer (PMUT) rotational IVUS imaging and pressure sensing system.In that regard, the main components of the IVUS imaging and pressuresensing system 100 are an IVUS and pressure sensing catheter 102, a PMUTcatheter compatible patient interface module (PIM) 104, an IVUS andpressure console or processing system 106, and a monitor 108 to displaythe IVUS images and any pressure information or data generated by theIVUS and pressure console 106.

At a high level, the IVUS and pressure sensing catheter 102 emitsultrasonic energy from an IVUS transducer at the tip of the catheter.The ultrasonic energy is reflected by tissue structures surrounding theIVUS transducer and the echo signals from the tissue are received andamplified by the IVUS transducer. The IVUS and pressure sensing catheter102 also detects data indicative of pressure within a target region ofthe patient with a pressure transducer at the tip of the device. Whileemitting ultrasonic energy and receiving echoes, or at intermittentintervals, the IVUS and pressure sensing catheter 102 takes pressurereadings within the target body region, often within the vasculature ofa patient. As described herein, the IVUS transducer and the pressuretransducer share an ASIC controller and the same communication and powercable extending toward the proximal end of the IVUS and pressure sensingcatheter.

The PIM 104 facilitates communication of signals between the IVUS andpressure console 106 and the IVUS and pressure sensing catheter 102 tocontrol the operation of the IVUS transducer and the pressuretransducer. Controlling the operation of the IVUS transducer includesgenerating control signals to configure the IVUS transducer and triggerthe transmitter circuit and transfer echo signals captured by the IVUStransducer to the IVUS and pressure console 106. With regard to the echosignals, the PIM 104 forwards the received signals and, in someembodiments, performs preliminary signal processing prior totransmitting the signals to the console 106. In examples of suchembodiments, the PIM 104 performs amplification, filtering, and/oraggregating of the data. In an embodiment, the PIM 104 also supplieshigh- and low-voltage DC power to support operation of the circuitrywithin the IVUS transducer, as well as the pressure sensor. At the sametime, the PIM 104 forwards pressure data received from the pressuretransducer and, in some embodiments, performs preliminary signalprocessing prior to transmitting the pressure data to the console 106.In examples of such embodiments, the PIM 104 performs amplification,filtering, and/or aggregating of the pressure data.

The IVUS and pressure console 106 receives the echo data from the IVUStransducer and receives pressure data from the pressure transducer byway of the PIM 104 and processes the data to create an image of thetissue surrounding the IVUS transducer and assesses the pressure withinthe target region. In some instances, the IVUS and pressure console 106is configured to calculate a fractional flow reserve (FFR) based on theobtained pressure measurements. The console 106 may also display theimage and/or pressure information, including the FFR on the monitor 108.

FFR is a currently accepted technique for assessing the severity of astenosis in a blood vessel, including ischemia-causing lesions. It isdefined as the ratio of the maximal blood flow in a stenotic artery,taken distal to the lesion, to normal maximal flow. Accordingly, tocalculate the FFR for a given stenosis, two blood pressure measurementsare taken: one measurement distal or downstream to the stenosis and onemeasurement proximal or upstream to the stenosis. FFR is a calculationof the ratio of the distal pressure measurement relative to the proximalpressure measurement. FFR provides an index of stenosis severity thatallows determination as to whether the blockage limits blood flow withinthe vessel to an extent that treatment is required. The more restrictivethe stenosis, the greater the pressure drop across the stenosis, and thelower the resulting FFR. FFR measurements can be used as a decisionpoint for guiding treatment decisions. The normal value of FFR in ahealthy vessel is 1.00, while values less than about 0.80 are generallydeemed significant and require treatment. Common treatment optionsinclude angioplasty, atherectomy, and stenting.

As discussed in greater detail below, the IVUS and pressure sensingcatheter 102 includes a PMUT ultrasound transducer along with itsassociated circuitry mounted near a distal tip of the catheter, a fourconductor electrical cable, and the appropriate electrical connector tosupport the rotational interface. The IVUS and pressure sensing catheter102 also detects data indicative of pressure within a target region ofthe patient with a pressure transducer near the distal tip of thecatheter.

The PIM 104 generates the required sequence of transmit trigger signalsand control waveforms to regulate the operation of the circuit andprocesses the amplified echo signals received over that same conductorpair. The PIM 104 also supplies the high- and low-voltage DC powersupplies to support operation of the IVUS and pressure sensing catheter102. An important feature of the PIM 104 is that it must deliver DCsupply voltages to the PMUT circuitry of the catheter 102 across arotational interface. This requirement largely precludes the option of arotary transformer, commonly used for traditional rotational IVUSsystems, since a transformer can only convey AC signals from the primaryto the secondary side. Practical options for delivering DC power acrossa rotating interface include the use of slip-rings and/or theimplementation of the active spinner technology described in U.S. PatentApplication Publication No. 2010/0234736, which is hereby incorporatedby reference in its entirety.

Referring now to FIG. 2, shown therein is a diagrammatic, partialcutaway perspective view of the rotational IVUS and pressure sensingcatheter 102 according to an embodiment of the present disclosure. Inthat regard, FIG. 2 shows additional detail regarding the constructionof the IVUS and pressure sensing catheter 102. In some respects, thiscatheter is similar to traditional rotational IVUS catheters, such asthe Revolution® catheter available from Volcano Corporation anddescribed in U.S. Pat. No. 8,104,479, or those disclosed in U.S. Pat.Nos. 5,243,988 and 5,546,948, each of which is hereby incorporated byreference in its entirety. In that regard, the IVUS and pressure sensingcatheter 102 includes an imaging core 110 and an outer catheter/sheathassembly 112. The imaging core 110 includes a flexible drive shaft thatis terminated at the proximal end by a rotational interface 114providing electrical and mechanical coupling to the PIM 104 of FIG. 1.The distal end of the flexible drive shaft of the imaging core 110 iscoupled to a transducer housing 116 containing the PMUT and associatedcircuitry, which are described in greater detail below. Thecatheter/sheath assembly 112 includes a hub 118 that supports therotational interface and provides a bearing surface and a fluid sealbetween the rotating and non-rotating elements of the catheter assembly.The hub 118 includes a luer lock flush port 120 through which saline isinjected to flush out the air and fill the inner lumen of the sheathwith an ultrasound-compatible fluid at the time of use of the catheter.The saline or other similar flush is typically required since air doesnot readily conduct ultrasound. Saline also provides a biocompatiblelubricant for the rotating driveshaft. The hub 118 is coupled to atelescope 122 that includes nested tubular elements and a sliding fluidseal that permit the catheter/sheath assembly 112 to be lengthened orshortened to facilitate axial movement of the transducer housing withinan acoustically transparent window 124 of the distal portion of thecatheter 102. In some embodiments, the window 124 is composed ofthin-walled plastic tubing fabricated from material(s) that readilyconduct ultrasound waves between the transducer and the vessel tissuewith minimal attenuation, reflection, or refraction. A proximal shaft126 of the catheter/sheath assembly 112 bridges the segment between thetelescope 122 and the window 124, and is composed of a material orcomposite that provides a lubricious internal lumen and optimumstiffness, but without the need to conduct ultrasound.

Referring now to FIG. 3, shown therein is a cross-sectional side view ofa distal portion of the catheter 102 according to an embodiment of thepresent disclosure. In particular, FIG. 3 shows an expanded view ofaspects of the distal portion of the imaging core 110. In this exemplaryembodiment, the imaging core 110 is terminated at its distal tip by ahousing 116 fabricated from stainless steel and provided with a roundednose portion 126 and an imaging cutout 128 for the ultrasound beam 130to emerge from the housing 116 and a pressure sensing cutout 129 for thepressure transducer 131 to detect pressure within the target anatomy.

In some embodiments, the flexible driveshaft 132 of the imaging core 110is composed of two or more layers of counter wound stainless steelwires, welded, or otherwise secured to the housing 116 such thatrotation of the flexible driveshaft also imparts rotation on the housing116. In the illustrated embodiment, the PMUT MEMS 138 includes aspherically focused transducer 142 and carries an application-specificintegrated circuit (ASIC) 144, also referenced herein as a controller.

The controller 144 is electrically coupled to the PMUT MEMS 138 throughtwo or more connections. In that regard, in some embodiments of thepresent disclosure the controller 144 includes an amplifier, atransmitter, and a protection circuit associated with the PMUT MEMS. Insome embodiments, the controller 144 is flip-chip mounted to thesubstrate of the PMUT MEMS 138 using anisotropic conductive adhesive orsuitable alternative chip-to-chip bonding method. When assembledtogether the PMUT MEMS 138 and the controller 144 form a controller/MEMShybrid assembly 146 that is mounted within the housing 116.

An electrical cable 134 with optional shield 136 is attached to thecontroller/MEMS hybrid assembly 146 with solder 140. The electricalcable 134 extends through an inner lumen of the flexible driveshaft 132to the proximal end of the imaging core 110 where it is terminated tothe electrical connector portion of the rotational interface 114 shownin FIG. 2.

Embodiments of the present disclosure identify a four wire electricalinterface that offers a wide array of benefits, with minimal compromiseto the performance of the circuit and transducer, while maintaining asmall cable dimension that can be readily accommodated by a rotationalIVUS catheter. One implementation of such an arrangement for theelectrical cable uses four electrical conductors, twisted together intoa symmetrical quad and treated as two diagonal conductor pairs. In fact,a twisted quad occupies only a slightly larger cylindrical space (20%larger diameter) compared to a twisted pair of the same size conductors.

In such a twisted quad cable embodiment, one diagonal pair of conductorsprovides a balanced transmission line that serves the following multiplepurposes: (1) conducting the balanced signal, such as data orinformation signals from the IVUS transducer and pressure transducer,from the controller amplifier output to the PIM amplifier input, (2)carrying the transmit trigger pulses as a balanced differential signalfrom the PIM transmit trigger circuitry to the transmitter and timingcircuitry included on the controller, (3) supplying low voltage DC poweras the common mode voltage on the conductor pair (referenced to theground conductor of the second pair), (4) providing receiver timingsignals to turn the amplifier circuitry on and off as needed to minimizepower dissipation in the controller, and (5) creating a serialcommunication channel to support advanced features such asprogrammability. The second diagonal pair of conductors carries the highvoltage supply and ground. The high voltage/ground pair, besides simplyproviding those DC voltages, also contributes a significant distributedcapacitance that stores energy to be used by the pulser circuit when itdelivers a high power transmit pulse to the transducer. In practice,when the transmitter is triggered to generate a high power pulse to thetransducer, it also launches a traveling wave as a balanced signal ontothe high voltage/ground conductor pair. When the traveling wave reachesthe PIM, the PIM supplies the charge needed to replenish what has beendrawn from that conductor pair by the transmit pulse. This cableconfiguration provides all of the required functions, using a four wireinterface with all signals transmitted over balanced lines, eachterminated with the appropriate characteristic impedance. The balanced,terminated transmission lines provide reduced generation andsusceptibility to EMI, low distortion of the transmit waveform, highspeed communication, minimal distortion of the amplifier frequencyresponse, and other electrical advantages. In some embodiments, thecable includes an optional shield around the twisted quad to furtherprotect the signal lines from EMI, to reduce electromagneticinterference emitted from the signal lines, and to provide addedmechanical integrity.

An alternative cable design according to the present disclosure,offering many of the same advantages described previously in conjunctionto the twisted quad configuration, is a shielded, twisted triplet. Inthis case, two conductors of the twisted triplet serve the multiplefunctions described previously for the first pair of conductors of thetwisted quad. The ground conductor serves as the shield, while the highvoltage is carried by the third conductor of the twisted triplet. Sincethe shield is symmetrical with respect to the conductors of the twistedtriplet, there is minimal differential interference signal coupled fromthe shield to the balanced signal lines that carry the amplifier output.Likewise, by symmetry, there is minimal coupling of interference on thehigh voltage conductor into the balance signal lines. Furthermore, thereis typically very little high frequency noise on the high voltage signalline, except for a brief transient during and immediately after atransmit pulse. Most of that high frequency transient will havedissipated by the time the earliest echo signals of interest return fromthe vessel tissue. The shielded twisted triplet is a highlymanufacturable configuration, with the triplet forming an inherentlystable and symmetrical bundle, and with the shield providing mechanicalintegrity for the cable and protection from external interference.

In the illustrated embodiment, the controller/MEMS hybrid assembly 146is secured in place relative to the housing 116 by an epoxy 148 or otherbonding agent. The epoxy 148 also serves as an acoustic backing materialto absorb acoustic reverberations propagating within the housing 116 andas a strain relief for the electrical cable 134 where it is soldered tothe controller/MEMS hybrid assembly 146. The pressure transducer 131electrically communicates with the controller 144 via leads 133extending therebetween. The controller 144 provides power to thepressure transducer via the leads. Accordingly, the controller 144,disposed at the distal end of the catheter, communicates with both thePMUT MEMS 138 and pressure transducer 131.

The pressure transducer 131 is mounted to measure pressure outside ofthe imaging core 110, and in a preferred embodiment, is a pressuresensor configured to sense pressure within the vasculature of a patientundergoing treatment. The pressure transducer 131 is electricallyconnected to the controller 144 which can process, amplify, or conditionanalog signals from the sensor and transmit corresponding data signalsto the proximal end of the catheter.

For this embodiment and other embodiments disclosed herein, the pressuretransducer 131 may comprise a rigid housing 135 at least partiallysurrounding and supporting any type of pressure sensitive transducer.The housing 135 permits the sensor to be sufficiently stress resistantto maintain functionality while embedded within or on the imaging core110. For example, the pressure transducer 131 may comprise a capacitivesensor, a piezoresistive pressure transducer, a fiber optic pressuresensor such as disclosed in U.S. Pat. Nos. 8,298,156 and 8,485,985 andU.S. Patent Application Publication Nos. 2013/0303914 and 2013/0131523(each incorporated by reference herein in their entirety), a sensor witha silicon backbone, or any other type of pressure sensor having therequisite durability and stress resistance. In some instances, thepressure transducer 131 includes an array or plurality of sensorelements (e.g., a capacitive pressure sensor array). In someembodiments, the pressure transducer 131 includes a sensor diaphragmassembly. In some embodiments, the sensor diaphragm assembly includes abody having a recess covered by a flexible diaphragm configured tomeasure fluid pressure. The diaphragm may flex in response to variationsin pressure around the diaphragm, thereby reflecting variations in bloodpressure, for example. The pressure transducer 131 can then measure andtransmit the variations in pressure imparted on the diaphragm assembly.

The sheath 112 includes an open end or apertures that allow the pressurewithin the sheath to substantially equal the pressure outside thesheath. As such, the pressure measured in the sheath by the pressuretransducer 131 is indicative of pressure outside the sheath.

Referring now to FIGS. 4-6, shown therein are additional aspects of thePMUT MEMS component 138 and controller 144 that form the controller/MEMShybrid assembly 146. In addition, FIG. 6 shows the pressure transducer131 attached to the controller 144 via three leads 133 connected to bondpads 182, 184, and 186. The MEMS component 138 in the embodiment ofFIGS. 4-6 is a paddle-shaped silicon component with the piezoelectricpolymer transducer 142 located in the widened portion 149 of thesubstrate located at the distal end of the MEMS component 138. Thenarrow portion of the substrate positioned proximal of the widenedportion 149 is where the controller 144 is mounted to the MEMS component138. In that regard, the MEMS component 138 includes ten bond pads, withbond pads 150, 151, 152, 154, 156, and 158 of the MEMS 138 configured tomatch up respectively with six bond pads 172, 170, 180, 178, 176, and174 on the controller 144 (shown in FIG. 6) when the controller isflip-chip mounted onto the MEMS 138. The flip-chip mounting isaccomplished using anisotropic conductive adhesive, gold-to-goldthermosonic bonding, and/or other suitable methods. Solder reflow is notconvenient for this application in some instances, since the copolymertransducer element is subject to depoling at temperatures as low as 100°C., well below conventional soldering temperatures. Anisotropicconductive adhesive can be cured at temperatures below 100° C., as longas the cure time is increased to account for the low cure temperature.In this embodiment, the bond pads 152, 154, 156, and 158 are coupled tobond pads 162, 164, 166, and 168 by conductive traces included on theMEMS substrate, with the bond pads 162, 164, 166, and 168 serving asterminations for the four conductors of the electrical cable 134, shownin FIG. 3. In that regard, the four conductors of the electrical cable134 are soldered or otherwise fixedly attached to bond pads 162, 164,166, and 168, which are electrically coupled with the bond pads 152,154, 156, and 158. In other embodiments, the four conductors of theelectrical cable 134 are soldered or otherwise fixedly attached directlyto the controller bond pads 174, 176, 178, and 180. The controller alsoincludes three bond pads 182, 184, and 186 connectable to the pressuretransducer 131. Conductive leads extend from the bond pads 182, 184, and186 to associated bond pads disposed on the pressure transducer 131.

Referring now to FIG. 7, shown therein is a cross-sectional side view ofa distal portion of an imaging core 200 according to another embodimentof the present disclosure. The imaging core 200 may be similar to theimaging core 110 of catheter 102 described above. In that regard, theimaging core 200 includes features and functionality similar to thosediscussed above with respect to imaging core 110. Accordingly, the samereference numerals have been utilized to refer to analogous features.For example, the imaging core 200 includes a MEMS 138 having atransducer 142, such as an IVUS transducer, formed thereon and acontroller 144 electrically coupled to the MEMS 138. However, in theexemplary configuration of FIG. 7, the controller 144 and the MEMS 138components are wire-bonded together, mounted to the transducer housing116, and secured in place with epoxy 148 or other bonding agent to forma controller/MEMS hybrid assembly 146. The leads of the cable 134 aresoldered or otherwise electrically coupled directly to the controller144 in this embodiment. The controller 144 includes leads 133 extendingto the pressure transducer 131. In some embodiments of thisconfiguration, the MEMS component 138 is a truncated version of thepaddle-shaped device shown in FIGS. 4 and 5, with the narrow “handle”portion of the paddle removed. One advantage of the wire-bondingapproach is that the MEMS component carrying the transducer 142 can bemounted at an oblique angle with respect to the longitudinal axis of thehousing 116 and imaging core 200 such that the ultrasound beam 130propagates at an oblique angle with respect to a perpendicular to thecentral longitudinal axis of the imaging core. This tilt angle helps todiminish the sheath echoes that can reverberate in the space between thetransducer and the catheter sheath 112, and it also facilitates Dopplercolor flow imaging as disclosed in U.S. patent application Ser. No.13/892,108, published as U.S. Patent Application Publication No.2013/0303907 on Nov. 14, 2013 and U.S. patent application Ser. No.13/892,062, published as U.S. Patent Application Publication No.2013/0303920 on Nov. 14, 2013, each of which is hereby incorporated byreference in its entirety.

FIG. 8 shows another exemplary embodiment of a portion of an IVUS arrayand pressure sensing catheter 600. The portion shown may be used at adistal end of an imaging and pressure sensing catheter as describedherein. FIG. 8 depicts an ultrasound scanner assembly 601 its flat form.When disposed on a catheter, the assembly 601 is rolled into acylindrical form. The assembly 601 includes a transducer array 602,transducer control circuits 604 (including controllers 604 a and 604 b),and a pressure senor 605 attached to a flex circuit 606. The controlcircuits correspond to the controller described above.

The transducer array 602 includes a plural of ultrasound transducers 603and replaces the single IVUS transducer described in other embodiments.The transducer array 602 may include any number and type of ultrasoundtransducers 603, although for clarity only a limited number ofultrasound transducers are illustrated in FIG. 8. In an embodiment, thetransducer array 602 includes 64 individual ultrasound transducers 603.In a further embodiment, the transducer array 602 includes 32 ultrasoundtransducers. Other numbers are both contemplated and provided for. In anembodiment, the ultrasound transducers 603 of the transducer array 602are piezoelectric micromachined ultrasound transducers (PMUTs)fabricated on a microelectromechanical system (MEMS) substrate using apolymer piezoelectric material, for example as disclosed in U.S. Pat.No. 6,641,540, which is hereby incorporated by reference in itsentirety. In alternate embodiments, the transducer array includespiezoelectric zirconate transducers (PZT) transducers such as bulk PZTtransducers, capacitive micromachined ultrasound transducers (cMUTs),single crystal piezoelectric materials, other suitable ultrasoundtransmitters and receivers, and/or combinations thereof.

In some embodiments, the transducer array 602 forms a part of apiezoelectric zirconate transducer (PZT) solid-state IVUS imagingdevice. In some embodiments, the catheter 600 incorporates capacitivemicromachined ultrasonic transducers (CMUTs), and/or piezoelectricmicromachined ultrasound transducers (PMUTs). The IVUS imaging andpressure detecting catheter 600 may be associated with the patientinterface module (PIM) 104, the IVUS and pressure console or processingsystem 106, and/or the monitor 108 (FIG. 1).

In the illustrated embodiment, the assembly 601 having 64 ultrasoundtransducers 603 and at least one pressure sensor 605 includes ninetransducer control circuits 604, of which five are shown. Designsincorporating other numbers of transducer control circuits 604 including8, 9, 16, 17 and more are utilized in other embodiments. In someembodiments, a single controller is designated a master controller andconfigured to receive signals directly from the electrical cable 134.The remaining controllers are slave controllers. In the depictedembodiment, the master controller 604 a does not directly control any ofthe IVUS transducers 603, but drives the pressure transducer 605. Inother embodiments, the master controller 604 a drives the same number ofIVUS transducers 603 as the slave controllers 604 b while driving thepressure transducer 605 or drives a reduced set of transducers 603 ascompared to the slave controllers 604 b. In the illustrated embodiment,a single master controller 604 a and eight slave controllers 604 b areprovided. Eight transducers are assigned to each slave controller 604 b.Such controllers may be referred to as 8-channel controllers based onthe number of transducers they are capable of driving.

The master controller 604 a generates control signals for the slavecontrollers 604 b based on configuration data and transmit triggersreceived via the electrical cable 134 and generates control signals forthe pressure transducer 605. The master controller 604 a also receivesecho data from slave controllers 604 b and from the pressure transducer605 and retransmits it on the electrical cable 134. To do so, in someembodiments, the master controller 604 a includes an echo amplifier (notshown). In this configuration, the master controller 604 a receivesunamplified or partially amplified echo data and performs the necessaryamplification for driving the echo data along conductors of theelectrical cable 134. This may provide additional room for a largerhigh-fidelity amplifier.

In an embodiment, the flex circuit 606 provides structural support andphysically connects the transducer control circuits 604 and thetransducers 603 and 605. In an embodiment, the flex circuit 606 furtherincludes conductive traces 610 formed on the film layer. Conductivetraces 610 carry signals between the transducer control circuits 604 andthe transducers 603 or 605 and provide a set of pads for connecting theconductors of electrical cable 134. Suitable materials for theconductive traces 610 include copper, gold, aluminum, silver, tantalum,nickel, and tin and may be deposited on the flex circuit 606 byprocesses such as sputtering, plating, and etching. In an embodiment,the flex circuit 606 includes a chromium adhesion layer. The width andthickness of the conductive traces are selected to provide properconductivity and resilience when the flex circuit 606 is rolled. In thatregard, an exemplary range for the thickness of a conductive trace 610is between 10-50 μm. For example, in an embodiment, 20 μm conductivetraces 610 are separated by 20 μm of space. The width of a conductivetrace 610 may be further determined by the size of a pad of a device orthe width of a wire to be coupled to the trace. Additional details ofthe flex circuit may be found in U.S. patent application Ser. No.14/137,269, published as U.S. Patent Application Publication No.2014/0187960 on Jul. 3, 2014, incorporated herein by reference.

As the circuit may be rolled to form the finished scanner assembly, thecontrol circuits 604, including both master and slave controllers, maybe shaped accordingly. This may include a control circuit 604 edgeconfigured to interface with an edge of an adjacent control circuit 604.In some embodiments, the control circuits 604 include interlocking teeth612 a and 612 b. For example, control circuits 604 may be formed with arecess and projection 612 a that interlocks with a recess and projection612 b of an adjacent control circuit 604 to form a box joint or fingerjoint. In some embodiments, a control circuit 604 includes a chamferededge 614, either alone or in combination with a recess and projection.The chamfered edge 614 may be configured to abut an edge of an adjacentcontrol circuit 604. In some such embodiments, the edge of the adjacentcontroller is chamfered as well. In some embodiments, each of thecontrollers 604 interlocks with two adjacent controllers utilizing asimilar recess and projection interface. Other combinations, includingembodiments utilizing a number of different mechanisms, are contemplatedand provided for. For example, in an embodiment, edges of slave controlcircuits interfacing with a master control circuit have a recess andprojection configuration with a chamfered region while edges of slavecontrol circuits interfacing with other slave control circuits have arecess and projection configuration without a chamfered region. Edgeconfigurations that interlock adjacent control circuits 604 may allowfor closer control circuit spacing 604 and a reduced diameter in therolled configuration. Such configurations may also interlock to create arigid structure and thereby provide additional structural support forthe rolled scanner assembly.

The pressure transducer 605 is disposed in a distal position on thecatheter 600 and is disposed at or beyond the top edge of the flexcircuit 606 so as to not interfere with operation of the IVUStransducers 603. In this example, the pressure transducer 605 is undercontrol of the master control circuit 604 a. Conductive traces, similarto other conductive traces described herein, extend from the mastercontrol circuit 604 a to the pressure transducer 605. Data orinformation obtained by the pressure transducer 605 may be communicatedto the control circuit 604 a, may receive some level of processing,amplification, or other treatment at the control circuit 604 a, and maythen be communicated on the same electrical conductors of thecommunication cable 134 as the signals relating to information from theIVUS transducers 603. In one aspect, the control circuit 604 a candigitize the one or more of the IVUS or pressure sensor signals prior totransmission.

FIG. 9 shows an exemplary catheter as used herein on a monorail pressuresensing catheter 700, where the catheter 700, including the controller144, the ultrasound transducer array 142, and the pressure sensor(s) 131are disclosed on or about the catheter, and are advanced to a patient'starget region over a guidewire 702.

An exemplary method of using the device disclosed herein is inferred byall the teachings herein as would be apparent to one of ordinary skillin the art and explicitly disclosed in the following paragraphs. Thecatheter is advanced through the vessel toward a target region or areaof interest in the patient. This may be a target area forming a part ofthe patient's vasculature, but may also be other parts of the patient'sbody. In some embodiments, the catheter is advanced over a guidewire,such as the guidewire 702 in FIG. 9.

With the catheter in the target region, the IVUS transducer and thepressure transducer sensors may be activated to obtain informationrelating to the target region. In some embodiments, this may be used toobtain information relating to stenosis in a vessel. The IVUS transducermay be used to image the target region of the patient, and the pressuretransducer may be used to measure pressure within the vessel. This mayoccur simultaneously or at separate times depending on the arrangementof the system. Signals representing the ultrasound imaging and thepressure are communicated from the transducers to the controller orASIC. The pressure or flow information may be transmitted via the sameelectrical cable, and may be communicated via the same conductor fromthe controller to the PIM and ultimately to the console 106, which maybe presented on the display 108 to the clinician. In some embodiments,the information representing the ultrasound imaging and the pressure arecommunicated from the controller to the PIM in real time. In otherinstances, the information is stored on the controller and then sentlater.

With both ultrasound transducers and pressure transducers on the samecatheter, the systems, devices, and methods herein are capable ofcarrying out both imaging and pressure sensing. In one example, thecombination catheter may be used to perform an IVUS pullback to imagethe vessel and, either during the pullback or at a separate timeinterval, may be used to sense pressure in the vessel. Accordingly,using a single catheter, medical personnel may be able to receive moreinformation relating to a patient's condition than could otherwise beobtained. In addition, since the signal from the ultrasound transducersand pressure transducers are communicated along the catheter usingshared conductors and other electrical components, such as the sameconductors in the communication cable 134, the catheter may bemaintained at a size small and effective for assessing even smallvessels of the vasculature. Because of the additional information thatmay be obtained from a single catheter, medical personnel may moreefficiently assess a patient. In some instances, this reduction inassessment time may also result in reduced time to actual treatment,reducing costs to the patient. In addition, due to the sharedcomponents, the overall diameter of the catheter may be smaller thancould otherwise be achieved. In addition, some manufacturing steps maybe eliminated when compared to manufacturing with distinct IVUS imagingand pressure transducers.

Persons skilled in the art will recognize that the apparatus, systems,and methods described above can be modified in various ways.Accordingly, persons of ordinary skill in the art will appreciate thatthe embodiments encompassed by the present disclosure are not limited tothe particular exemplary embodiments described above. In that regard,although illustrative embodiments have been shown and described, a widerange of modification, change, and substitution is contemplated in theforegoing disclosure. It is understood that such variations may be madeto the foregoing without departing from the scope of the presentdisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the presentdisclosure.

What is claimed is:
 1. An apparatus, comprising: an intravascularcatheter configured to be positioned within a blood vessel of a patient,wherein the intravascular catheter comprises: a flexible drive shaftconfigured to be rotated; and a sensing assembly coupled to a distalportion of the flexible drive shaft, and wherein the sensing assemblycomprises: a housing; a single ultrasound transducer element; and asingle pressure sensor.
 2. The apparatus of claim 1, wherein singleultrasound transducer element and the single pressure sensor areoriented in different directions.
 3. The apparatus of claim 1, whereinthe single pressure sensor is positioned distal of the single ultrasoundtransducer element.
 4. The apparatus of claim 1, the single pressuresensor forms a distal-facing surface of the sensing assembly.
 5. Theapparatus of claim 1, wherein the housing comprises a nose with arounded portion, wherein the rounded portion is interrupted by a cutout,wherein the pressure sensor is positioned proximate to the cutout. 6.The apparatus of claim 1, wherein the sensing assembly further comprisesan adhesive disposed within the housing and in contact with the singleultrasound transducer element and a single pressure sensor is mounted onthe adhesive.
 7. The apparatus of claim 6, wherein the sensing assemblyfurther comprises at least one lead coupled to the single pressuresensor and configured carry signals associated with single pressuresensor, wherein the adhesive is in contact with the at least one lead.8. The apparatus of claim 1, wherein the sensing assembly furthercomprises at least one lead coupled to the single pressure sensor andconfigured carry signals associated with single pressure sensor, whereinthe at least one lead is positioned within the housing.
 9. The apparatusof claim 8, wherein the at least one lead extends only within thehousing.
 10. The apparatus of claim 8, wherein at least one lead extendsaround the single ultrasound transducer element.
 11. The apparatus ofclaim 10, wherein the single ultrasound transducer element comprises afirst surface and an opposite, second surface, wherein the first surfaceis configured to emit an ultrasound beam, and wherein the at least onelead extends proximate to the second surface.
 12. The apparatus of claim8, wherein the sensing assembly further comprises: a controllerconfigured for communication to the single pressure sensor via the leastone lead.
 13. The apparatus of claim 12, wherein the at least one leadextends lengthwise within the housing between the controller and thesingle pressure sensor.
 14. The apparatus of claim 12, wherein thecontroller comprises a first bond pad configured to establish thecommunication with the single pressure sensor.
 15. The apparatus ofclaim 14, wherein the controller is configured for communication withthe single ultrasound transducer element, wherein the controllercomprises a second bond pad configured to establish the communicationwith the single ultrasound transducer element.
 16. The apparatus ofclaim 1, wherein the intravascular catheter further comprises a sheath,wherein the sensing assembly is positioned within the sheath, andwherein the sheath comprises at least one of an open end or an aperturesuch that a pressure measured by the pressure sensing within the sheathis indicative of a pressure outside of the sheath.